ATPase activity of guinea pig heart muscle

Riassunto L'Autore ha studiato l'influenza della concentrazione degli ioni Ca⁺⁺ e Mg⁺⁺ sull'ATPasi degli atri e dei ventricoli di cuore di cavia. Tale attività è maggiore a pH 9,2 che a pH 6,8. Mentre il Ca⁺⁺ influisce differenziando decisamente le attività degli atri da quelle dei ventricoli, il Mg⁺⁺ accentua piuttosto una differenza tra la parte destra e la sinistra. Il calore distrugge quasi completamente l'attività enzimatica dopo una permanenza a 60° per 20 min.     

Antagonism of dibutyryl-guo-3′:5′-P and atropine on stomach smooth muscle contraction

Riassunto Viene mettona in evidenza l'effetto contratturante del Guo-3:5-P sulla muscolatura liscia di stomaco di ratto in vitro. Tale effetto è antagonizzato dall'Atropina e scompare dopo vagotomia. Una possibile interazione fra il Guo-3:5-P e la trasmissione colinergica sembra così emergere da questi primi risultati.     

The effect of urethane on histamine-induced contraction of guinea-pig tracheal smooth muscle

Summary Urethane possesses a direct depressant action on histamine-induced contractions of guinea-pig tracheal smooth muscle both in vivo and in vitro.     

The role of myosin phosphorylation in the contraction-relaxation cycle of smooth muscle

Summary Considerable evidence from a variety of experimental procedures indicates that the phosphorylation of myosin is involved in the regulation of contractile activity in smooth muscle. Phosphorylation of the 20,000-dalton myosin light chains is required to initiate crossbridge cycling and this is consistent with the observation that the actin-activated Mg²⁺-ATPase activity of myosin is phosphorylation-dependent. In the simplest interpretation of this process it may be proposed that phosphorylation acts as an on-off switch. Clearly this cannot explain the observed complexity of smooth muscle contractile behavior and such may imply either that additional mechanisms are involved or that the role of myosin phosphorylation is not fully appreciated. Recently it has been shown that monomeric smooth muscle myosin can exist in a folded and an extended conformation and that each form is characterized by distinct enzymatic properties. Under appropriate solvent conditions phosphorylation of myosin favors the extended conformation. It is tentatively suggest that this, or an analogous, transition might be involved in the regulation of the smooth muscle contractile apparatus, and this possibility is discussed.The authors are supported by grants HL 23615 and HL 20984 from the National Institutes of Health.     

The effects of temperature on ATPase activity and force generation in skinned muscle fibers from the Pacific blue marlin (Makaira nigricans)

Summary ATPase activity and force generation have been measured simultaneously in isolated, demembranated muscle fibers of the Pacific blue marlin (Makaira nigricans) between 0 and 30°C. Tension generation is relatively independent of temperature above 15°C and falls with a Q₁₀ of <1.5 on decreasing the temperature to 0°C. In contrast, the Q₁₀ for ATPase activity is 2.2 over the range 0–30°C. The results are interpreted in terms of the cross bridge theory of contraction.     

The initiation of contraction by extracellular calcium in the smooth muscle of the guinea-pigTaenia coli

Zusammenfassung Die Ca-Wirkungen auf elektrische und mechanische Aktivität glatter Meerschweinchenmuskeln wurden untersucht. Die Resultate sprechen dafür, dass Kalziumionen, die während der Dauer des Aktionspotentials in die glatte Muskelzelle eintreten, am kontraktilen Elementarvorgang beteiligt sind.     

Differential response of myosin — ATPase activity and contraction properties of fast and slow rabbit muscles following denervation

Zusammenfassung Nachweis unterschiedlicher Kontraktionsgeschwindigkeiten bei schnellen und langsamen Kaninchenmuskeln sowie entsprechende Unterschiede in der Myosin-ATPase-Aktivität und im Spektrum niedermolekularer Proteine nach Denervation werden gezeigt.

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We are indepted to MissA. Krejová and Mrs.A. Herbrychová for their valuable and skillfull technical assistance.     

Evidence for a neurogenic ‘rebound’ contraction of the smooth muscle of the chicken proventriculus

Zusammenfassung Die Wirkung elektrischer Reizung einerseits vagal, andererseits transmural auf isolierte Muskelpräparate vom Hühnervormagen wurde untersucht und gefunden, dass eine nach Aufhören der Reizung beobachtete Nachkontraktion nicht als «rebound» zu betrachten ist, sondern cholinergische Züge zeigt.     

Time course of the regeneration of the endplate zone after autologous muscle transplantation

Reinnervation of transplanted muscles occurs in 2 steps. During the first 5 months the motor axon terminals innervate primarily the border of the original endplate zone, re-establishing its previous outline. In the next 4 months, by further ramifying of the axons, new nerve-muscle contacts are formed exclusively within the boundaries of this zone.     

Time course of the regeneration of the endplate zone after autologous muscle transplantation

Summary Reinnervation of transplanted muscles occurs in 2 steps. During the first 5 months the motor axon terminals innervate primarily the border of the original endplate zone, re-establishing its previous outline. In the next 4 months, by further ramifying of the axons, new nerve-muscle contacts are formed exclusively within the boundaries of this zone.     

Inhibition of erythrocyte ATPase activity by aclacinomycin and reverse effects of ascorbate on ATPase activity

We studied the effect of aclacinomycin on human erythrocyte membrane enzymes. Aclacinomycin inhibited ATPase, including Na-K-dependent ATPase, ouabain insensitive ATPase and Ca-ATPase. However acetylcholinesterase was not inhibited by aclacinomycin. The ATPase activities were not inhibited by aclacinomycin if ascorbate was added to the incubation mixture. However other reducing agents, alpha-tocopherol, superoxide dismutase and catalase had no effect on ATPase activity. Ascorbate may protect membrane proteins and lipids from peroxidate damage.     

Mechanical and biochemical characterization of the contraction elicited by a calcium-independent myosin light chain kinase in chemically skinned smooth muscle

Summary The contraction induced by a Ca²⁺-independent myosin light chain kinase (MLCK-) was characterized in terms of isometric force (F_o), immediate elastic recoil (SE), unloaded shortening velocity (V_us), shortening under a constant load and ATPase activity of chemically skinned smooth muscle preparations. These parameters were compared to those measured in a Ca²⁺-induced contraction to assess the nature of cross bridge interaction in the MLCK-induced contraction. F_o developed in chicken gizzard fibers as well as SE were similar in contractions elicited by either agent. V_us in the contraction induced by MLCK-(0.36 mg/ml) was similar though averaged 39.3±8.9% less than V_us induced by Ca²⁺ (1.6x10^–6M) in the control fibers. Addition of Ca²⁺ (1.6x10^–6M) to a contraction induced by MLCK-resulted in small increases in both F_o and V_us. Shortening under a constant load was similar for both types of contractions. The contraction induced by MLCK-was accompanied by an increased rate of ATP hydrolysis. The MLCK-induced contraction is thus kinetically similar though not identical to a contraction induced by Ca²⁺. We conclude that with respect to actin-myosin interaction, MLCK- and Ca²⁺-induced contractions are similar.     

Mechanical and biochemical characterization of the contraction elicited by a calcium-independent myosin light chain kinase in chemically skinned smooth muscle

The contraction induced by a Ca2+-independent myosin light chain kinase (MLCK-) was characterized in terms of isometric force (Fo), immediate elastic recoil (SE), unloaded shortening velocity (Vus), shortening under a constant load and ATPase activity of chemically skinned smooth muscle preparations. These parameters were compared to those measured in a Ca2+ -induced contraction to assess the nature of cross bridge interaction in the MLCK-induced contraction. Fo developed in chicken gizzard fibers as well as SE were similar in contractions elicited by either agent. Vus in the contraction induced by MLCK-(0.36 mg/ml) was similar though averaged 39.3 +/- 8.9% less than Vus induced by Ca2+ (1.6 X 10(-6) M) in the control fibers. Addition of Ca2+ (1.6 X 10(-6) M) to a contraction induced by MLCK-resulted in small increases in both Fo and Vus. Shortening under a constant load was similar for both types of contractions. The contraction induced by MLCK-was accompanied by an increased rate of ATP hydrolysis. The MLCK-induced contraction is thus kinetically similar though not identical to a contraction induced by Ca2+. We conclude that with respect to actin-myosin interaction, MLCK-and Ca2+ -induced contractions are similar.     

Intracellular recording of electrical activity in smooth muscle of the common bile duct

Zusammenfassung Im Rahmen vergleichender Untersuchungen an verschiedenen Typen spontan aktiver glatter Muskulatur wurde beim isolierten Ductus choledochus des Meerschweinchens durch intrazelluläre Messungen des Membranpotentials regelmässig eine mittelstarke Spontanaktivität, bestehend aus sekundenrhythmischen Oszillationen mit Spikes, moduliert durch langsamere Fluktuationen im Minuten-Rhythmus, gefunden.

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This work was supported by grant No. Go 130/13 from the Deutsche Forschungsgemeinschaft.     

Oxidative activity of limbic structures during sexual cycle in rats

Resumen Se ha estudiado el consumo de oxígeno de la amigdala y del hipocámpo en ratas hembras durante el ciclo sexual. La corteza cerebral se utilizó como control. Los resultados obtenidos indican que ambas estructuras límbicas sufren cambios ciclicos. La mayor actividad metabólica de la amigdala fué observada durante el estro en cambio el hipocampo tiene su mayor consumo de oxígeno durante el diestro.

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Supported by a grant of Fundacón Marqués de Urquijo.